The Delta N gamma electromagnetic transition form factors G*(M)(q(2)) and G*(E)(q(2))

摘要

A parameter-free, nonperturbative calculation of the DeltaNgamma electromagnetic transition amplitudes G(M)(*)(q(2)), G(E)(*)(q(2)), and the resonant multipole ratio R-EM(q(2)) equivalent to E-1+(3/2)(q(2)) is performed in terms of the well-known nucleon isovector Sachs form factor G V. Our methods are fully relativistic with conservation of the electromagnetic current guaranteed. We find that G(M)(*)(q(2)) decreases more rapidly than the nucleon dipole form factor when -q(2) greater than or similar to 1 GeV2/c(2) and that R-EM(q(2)) remains small even for very high four-momentum transfer implying that the perturbative QCD prediction R-EM(q(2)) --> 1 is purely asymptotic and is valid only for extremely high q(2). (C) 2004 Elsevier B.V. All rights reserved.